The majority of powered mobility vehicles for individuals who are physically handicapped are generally categorized into two principal groups, namely motor scooters and power chairs. A scooter typically has three wheels although four wheel versions have been known to exist. A pair of rear wheels are powered by a single electric motor and the passenger is seated forwardly of the rear axle.
In a power chair version of a conventional mobility device, the chair has four wheels, the front wheels generally not being powered but the rear wheels being driven by independent electric motors powered by batteries. The passenger is seated ahead of the rear wheels.
A number of deficiencies have been noted in conventional mobility devices of the scooter and chair types. Because the passenger is typically carried well forward of the driving, rear wheels, a major portion of the total vehicle weight is supported by the front wheels. This has several undesirable effects for such mobility devices.
In a three-wheeled scooter, the scooter body is very prone to tipping during the most moderate of turns of the vehicle. In the case of a four-wheeled power chair, the high weight loading, which exceeds 50% under some circumstances, makes the swiveling action of the front casters extremely difficult to achieve, particularly on surfaces such as gravel or deep carpet. In such cases, a large amount of power is needed to effect a turn of the device. When turning or steering the front wheels, the high power levels delivered to the drive wheels causes an abrupt and, at worst, uncontrollable surge and swerve in the direction of the turn when the initial resistance is overcome.
Due to these same weight distribution problems, a four-wheeled chair has difficulty following a straight track while moving along the side of a hill. The weight of the passenger between the front steering wheels and the rear driving and steering wheels, produces a moment which causes the chair to turn down-slope unless immediate and significant uphill steering power is applied.
As power chairs have become more common and the public acceptance of the mobility impaired in everyday endeavors has become a fact, the chair user has expected greater and greater achievements from such devices. Units of far greater power and range are now the norm. Because of the high power and torque available from conventional DC motors, adhesion and traction problems have become significant. Small footprint tires and poor weight distribution, as described, cause excessive tire slippage and spinning. This in turn produces limited traction under adverse weather or terrain conditions and provides greater diminished steering response.
To counteract any tendencies to tip forwardly or backwardly during acceleration or deceleration, the wheel base must be relatively long with the seat placed somewhere between the front and rear wheels. This placement causes a constant compromise between anti-tip stability and realistic wheel loading. Moreover, these compromises require the layout of these conventional vehicles in less than an optimum manner.
Finally, the geometry, drive characteristics and overall packaging of the scooter or power chair produce large turning radii. They also result in clumsy handling of the scooter or power chair in confined spaces.
Because of the problems and drawbacks of conventional scooter and power chair versions of mobility devices, a need exists for an improved vehicle which avoids these problems and drawbacks to provide high usable power, maximum weight distribution to the drive wheels and enhanced stability and more intuitive control of the chair. This provides for pivoting of the chair, i.e., rotation of the chair without translation, and rotation of the chair, i.e., pivotal and translational movements. The present invention satisfies this need.